postgreSQL 语法 "WHERE" 条件表示法 "(0,1)"

Question

我现在正在学习SQL中的数据透视，其中一个例子是：

CREATE EXTENSION IF NOT EXISTS tablefunc;
SELECT * FROM CROSSTAB($$
SELECT
meal_id,
DATE_TRUNC('month', order_date) :: DATE AS delivr_month,
COUNT(DISTINCT order_id) :: INT AS orders
FROM orders
WHERE meal_id IN (0, 1)
AND order_date < '2018-08-01'
GROUP BY meal_id, delivr_month
ORDER BY meal_id, delivr_month $$)
AS ct (meal_id INT,
"2018-06-01" INT,
"2018-07-01" INT)
ORDER BY meal_id ASC;

你能告诉我WHERE meal_id IN (0, 1)是什么意思吗？我试着寻找答案，但找不到任何好的解释。

如果你能帮我，我会非常感激的。谢谢你。。。

Answer 1

https://www.w3schools.com/sql/sql_in.asp

在括号内，您可以指定meal_id = 0单独检查并由OR连接的元素-操作员